A pumice raft spotted by a Royal New Zealand Air Force crew has pointed to a possible major undersea eruption somewhere in the Tonga-Kermadec volcanic arc in the Pacific Ocean.
The crew was on patrol on November 16 when it came across the mass of floating pumice on the ocean surface, about 80 nautical miles west of Minerva Reef, south of Fiji.
They reported the raft to GNS Science scientists, who then looked to satellite images to check where it came from.
"Normally you can go back and track them using the satellite images to compare where they first appeared and where are now," GNS volcanologist Brad Scott said.
"But unfortunately, because of weather and cloud, we are a little bit vague on where it might have come from."
It appeared the raft had moved north towards Fiji.
"We've asked the Air Force, if they're ever back up there, to revisit the area and also check the Monowai submarine volcano, which we know was erupting on November 10 and 11."
Scott said there was no connection between the mystery submarine eruption and the large quakes that had hit Kaikoura and Japan in recent days.